EP0390833A1 - Method for purification of tellurium and selenium alkyls. - Google Patents
Method for purification of tellurium and selenium alkyls.Info
- Publication number
- EP0390833A1 EP0390833A1 EP89900285A EP89900285A EP0390833A1 EP 0390833 A1 EP0390833 A1 EP 0390833A1 EP 89900285 A EP89900285 A EP 89900285A EP 89900285 A EP89900285 A EP 89900285A EP 0390833 A1 EP0390833 A1 EP 0390833A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- adduct
- alkyl
- tellurium
- purification
- cdbr
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C391/00—Compounds containing selenium
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C395/00—Compounds containing tellurium
Definitions
- This invention relates to methods for the purification of tellurium and selenium alkyls, particularly the dialkyls of these metals.
- Tellurium and selenium alkyls are important compounds used in the semiconductor industry, for example in the preparation of Cadmium Mercury Telluride (CMT) used in opto-electronic applications.
- CMT Cadmium Mercury Telluride
- the alkyls are decomposed, usually thermally to form the element, which may be itself deposited on a substrate, or combined with other elements in compounds. It is a very important requirement of such alkyls that they be extremely pure, as the presence of even minute quantities of impurities, eg at a ppm level can have a detrimental effect on the properties of the semiconductor.
- the present invention seeks to overcome the problems of prior art methods of purification of tellurium and selenium alkyls by novel routes using adducts, some of which are themselves novel.
- a method of purification of a tellurium or selenium alkyl characterised by forming an adduct of the alkyl with at least one compound of a Group 11 or 12 metal (Cu, Ag, Au, Zn, Cd, Hg) and thermally dissociating the said adduct to yield the alkyl.
- the at least one compound of a group 11 or 12 metal is an inorganic compound.
- the method is suitable for the purification of all tellurium and selenium alkyls, but is particularly suitable for the metal dialkyls.
- the alkyl group may be straight or branched chain, and is preferably a lower alkyl eg containing up to 4 carbon atoms. These lower alkyls are most useful for semiconductor production.
- Preferred Group 11 or 12 metals are cadmium, mercury and copper.
- the compound is preferably a halide or nitrate, most preferably halides, these being bromides, chlorides and iodides.
- the most preferred c ⁇ mpounts are therefore: Cul, CdI 2 , CdBr 2 , HgCl 2 , Cu 2 I 2 , Hgl 2 .
- the method is carried out in the following way:
- a solution of the alkyl in a suitable solvent is prepared, ani this is added to a solution of the metal compound in a suitable solvent, preferably an organic solvent.
- a suitable solvent preferably an organic solvent.
- Preferred solvents in both cases are polar aliphatic orpanic solvents containing 1 to 10 carbon atoms, preferably 1 to 5. It is desirable to use a solvent for the alkyl that is also capable of dissolving the metal compound.
- Suitable sovents for the alkyl include ethers, such as THF but especially diethyl ether; alcohols, especially ethanol: and nitriles especially acetonitrile These solvents are also suitable for the metal compound.
- the alkyl is dissolve! in an ether an! is added at an appropriate rate to a solution of the metal compound in an alcohol.
- the ammount of alkyl and metal compound used are in approximately stoichioimetric ratios.
- the adduct is thermally dissociated in vacuo to yield the pure alkyl which may be collected in a cooled receiver.
- Suitable dissociation temperatures will depend upon the adduct and are easily determined experimentally. Generally temperatures in the range 80° - 150°C are suitable.
- the preparation and subsequent manipulation of the adduct is performed under an inert atmosphere such as nitrogen.
- Alkyls purified by the process of the invention are in many instances in a state of purity suitable for their use directly in the preparation of semiconductors, for example the epitaxial deposit of CMT.
- Table 1 lists various adducts which were prepared using the method of the two preparative examples and some of their characteristics.
- Table 2 lists the microanalytical data for the various adducts.
- a solution of diethyltellurium (4.78g 0.025 g mol) was added . dropwise to a red solution of mercury (II) iodide (6.16g, 0.013 g mol) in ethanol ( 250 cm 3 ) to obtain a pale yellow crystalline product.
- the product was isolated from the reaction mixture by filtration under a nitrogen atmosphere and by successive washings with petroleum ether pre-cooled to 4°C. The crystals were pumped to remove any volatile impurities for 1 hour at room temperature.
- a solution of diethyltellurium (5.71g, 0.0307 g mol) was added dropwise to a solution of mercury (II) Chloride (7.39g, 0.0272 gmol) in diethyl ether (250 cm 3 ) to obtain a pale yellow crystalline product.
- the product was isolated from the reaction mixture by filtration under a nitrogen atmosphere and by siccessive washings with petroleum ether precooled to 4°C. The crystals were pumped to remove any votalite impurities for 1 hour at room temperature.
- the pure adduct (2.5 g) was heated to ca.125°C Pure di-isopropylt ⁇ llurium distilled and was collected in vacuo in a cold trap maintained at -196oC. Yield was 1.oo g. 65.56 % based on the weight of the adduct
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
Procédé de production d'alkyles et de dialkyles de tellure et de sélénium purifiés, consistant à réaliser un produit d'addition de l'alkyle avec au moins un composé d'un métal du groupe 11 ou 12, et à dissocier ledit produit d'addition afin de produire une forme purifiée du produit d'addition, et dans lequel on utilise le produit purifié dans les semiconducteurs tels que le tellure de mercure de cadmium pour des détecteurs à infrarouge.Process for the production of purified tellurium and selenium alkyls and dialkyls, comprising producing an alkyl adduct with at least one compound of a group 11 or 12 metal, and dissociating said product from addition to produce a purified form of the adduct, and wherein the purified product is used in semiconductors such as cadmium mercury telluride for infrared detectors.
Description
Method for Purification of Tellurium and Selenium Alkyls
This invention relates to methods for the purification of tellurium and selenium alkyls, particularly the dialkyls of these metals.
Tellurium and selenium alkyls are important compounds used in the semiconductor industry, for example in the preparation of Cadmium Mercury Telluride (CMT) used in opto-electronic applications. In many such uses the alkyls are decomposed, usually thermally to form the element, which may be itself deposited on a substrate, or combined with other elements in compounds. It is a very important requirement of such alkyls that they be extremely pure, as the presence of even minute quantities of impurities, eg at a ppm level can have a detrimental effect on the properties of the semiconductor.
Present methods of purification of tellurium and selenium alkyls generally involve fractional distillation and are unable to easily reach the abovementioned levels of purity. Another known method of purifying metal alkyls involves the formation of an adduct that has properties which allow it to be decomposed in such a way that the pure alkyl is formed as a decomposition product. The use of adducts in this way to purify tellurium and selenium alkyls is as yet unknown, although some work has been done to investigate various adducts of these alkyls. See for example G E Coates J Chem Soc (1951) pp 2003 - 2013. It is known that some of these adducts dissociate with relative ease, but none have been previously known to dissociate in such a way as to yield the pure alkyls.
The present invention seeks to overcome the problems of prior art methods of purification of tellurium and selenium alkyls by novel routes using adducts, some of which are themselves novel. According to the present invention there is provided a method of purification of a tellurium or selenium alkyl characterised by
forming an adduct of the alkyl with at least one compound of a Group 11 or 12 metal (Cu, Ag, Au, Zn, Cd, Hg) and thermally dissociating the said adduct to yield the alkyl. Preferably the at least one compound of a group 11 or 12 metal is an inorganic compound. The method is suitable for the purification of all tellurium and selenium alkyls, but is particularly suitable for the metal dialkyls. The alkyl group may be straight or branched chain, and is preferably a lower alkyl eg containing up to 4 carbon atoms. These lower alkyls are most useful for semiconductor production. Preferred Group 11 or 12 metals are cadmium, mercury and copper. The compound is preferably a halide or nitrate, most preferably halides, these being bromides, chlorides and iodides. The most preferred cσmpounts are therefore: Cul, CdI2, CdBr2, HgCl2, Cu2I2, Hgl2. Preferably the method is carried out in the following way:
(i) A solution of the alkyl in a suitable solvent is prepared, ani this is added to a solution of the metal compound in a suitable solvent, preferably an organic solvent. Preferred solvents in both cases are polar aliphatic orpanic solvents containing 1 to 10 carbon atoms, preferably 1 to 5. It is desirable to use a solvent for the alkyl that is also capable of dissolving the metal compound.
Suitable sovents for the alkyl include ethers, such as THF but especially diethyl ether; alcohols, especially ethanol: and nitriles especially acetonitrile These solvents are also suitable for the metal compound.
Typically the alkyl is dissolve! in an ether an! is added at an appropriate rate to a solution of the metal compound in an alcohol. Preferably the ammount of alkyl and metal compound used are in approximately stoichioimetric ratios.
(ii) When reaction appears to be complete, excess solvents may be separated by filtration from any precipitated product, or alternately or additionally the bulk of the solvent may be removed by evaporation. (iii) The solid adduct product is washed with an appropriate solvent, eg the ether used in the reaction, and excess volatiles removed in vacuo.
(iv) The adduct is thermally dissociated in vacuo to yield the pure alkyl which may be collected in a cooled receiver. Suitable dissociation temperatures will depend upon the adduct and are easily determined experimentally. Generally temperatures in the range 80° - 150°C are suitable.
It is preferred that the preparation and subsequent manipulation of the adduct is performed under an inert atmosphere such as nitrogen.
Appropriate conditions for the preparation of any particular tellurium or selenium alkyl can be easily determined experimentally generally following the procedure outlines above. Alkyls purified by the process of the invention are in many instances in a state of purity suitable for their use directly in the preparation of semiconductors, for example the epitaxial deposit of CMT.
The invention will now be described by way of example only. Table 1 below lists various adducts which were prepared using the method of the two preparative examples and some of their characteristics. Table 2 below lists the microanalytical data for the various adducts.
Certain of the adducts described below are novel, ie;
((C2H5)2Te)2CdI2
(G2H5)2Te(CdBr2)2
((C2H )2Te)2CdBr2 ((iso-C3H7)2Te)2CdI2
((iso-C3H7)2Te)2Cdbr2
Table 2: Preparation of Adducts of R2Te with Group 11 & 12 Meta] compounds
Dialkyltellurium Metal Compd Solvent Employed* R2Te: MXn Analysis (%) (R2Te) MXn ratio in found (theoretical) the adduct
Diethyltellurium Cdl2 Ethanol 2:1 12.2 (13.0) 2.5 (2.7)
(C2H5)2Te CdBr2 Ethanol 1:2 5.7 (• 6.5) 1.1 (1.3)
CdBr2 Ethanol 2:1 14.2 (14.9) 3.1 (2.8)
HgCl2 Diethylether 1:1 10.4 (10.5) 2.2 (2.2)
Hgl2 Ethanol 2:1 11.9 (11.6) 2.2 (2.6)
Cu2I2 Acetonitrile 1:1 12.7 (12.7) 2.6 (2.6)
Di-isopropyltellurium Cdl2 Ethanol 2:1 18.4 (18.1) 3.6 (3.5) ((CH3)2CH}2Te CdBr2 Ethanol 2:1 14.7 (14.8) 2.8 (2.9) ((CH3)2CH}2Te CdI2 ϋthnnol 1:1 12.4 (12.8) 2.4 (2.6)
* In each case, an ethereal solution of R2Te was added to the metal halide in the solvent shown.
Preparative Example 1
Purification of diethyltelluri u m using cadm ium iodide
A solution of dietlyltellurlum (25.6 g, 0.1373 gmol) In diethylether (50 cm3) Has added dropwise to a solution of cadmium Iodide (24.1 g, 0.065 gmol) in ethanol (350 cm3) to obtain a white precipitate which dissolved on warming to 50ºC. The reaction mixture was cooled and stirred at room temperature for 30 minutes. The volume Has reduced to ca 100 cm3 in vacuo and the product was obtained as white crystals on cooling to -30°C overnight. The crystals were isolated from the reaction mixture by filtration under a nitrogen atmosphere and by successive washings with petroleum ether cooled to 4ºC. The crystals were pumped to remove any volatile impurities for lh at room temperature.
Microanalytical data suggested that the product had a limiting empirical formula (Et2Te)2CdI2. The pure adduct, (Et2Te)2CdI2 (34.95 g, 0.0473 gmol) was then heated to 100°C. Pure dlethyltellurium distilled and was collected in vacuo in a cold trap (11.00 g, 0.0592 gmol, 62.52% yield). The adduct was found to dissociate between 85-90°C.
Prepara ti ve Example 2
Purificat ion o f diethyltellurium using Copper (I) iodide
A solution of diethyltellurium (6.6 g, 0.0355 gmol) in diethylether (25 cm3) was added dropwise to a solution of copper(I) iodide (3.5 g, 0.0183 gmol) in acetonitrile (50 cm3).
A pale pink mlcrocrystalline precipitate formed during the addition. The excess diethyltellurium and acetonitrile were removed by filtration under a nitrogen atmosphere and by successive Washings with petroleum ether cooled to 4ºC. The adduct obtained was pumped for lh at room temperature to remove any volatile impurities, Microanalytlcal studies revealed a limiting empirical formula (Et2Te)CuI.
The adduct, (Et2Te)CuI was then heated to 150*0 in vacuo ,
Pure diethyltellurium distilled and was collected in a pold trap. No sublimation of the adduct was found to occur up to 150°C. The dissociation of the adduct was found to occur between 110-130ºC.
Preparative Example 3
Purification of di-isopropyltellurium using cadmium iodide
A solution of di-isopropyl tellurium (26.34g, 0.1253 g mol.) in diethyl ether (150 cm3) was added dropwise to a solution of cadmium iodide (22.50g, 0.0614 g mol.) in ethanol (200 cm3). The reaction mixture was cooled to -30°C overnight and the product obtained as white needle crystals. The crystals were isolated from the reaction mixture by filtration under a nitrogen atmosphere and by successive washings with petroleum ether, pre-cooled to 4°C.
The crystals were pumped for 1 hour at room temperature to remove any volatile impurities. Overall yield 25.14g (51.47%). Microanalysis of the crystals suggested that the product had a limiting empirical formula (iPrTe)2(CdI2).
The pure adduct (iPrTe)2(CdI2), (25.14g, 0.0316 g mol.) was heated to about 175°C. Pure di-isopropyl tellurium distilled and was collected in vacuo in a cold trap (7.17g, 0.0335 g mol., 53% yield). The adduct was found to dissociate between 125°C-135°C.
Preparative Example 4
Purification of diethyltellurium using Cadmium Bromide
A solution of diethyltellurium (23.32g, 0.1256 g mol) in 3 diethylether (150 cm ) was added dropwise to a solution of cadmium bromide (CdBr2, 4H2O, 88.62g, 0.2574 g mol) in ethanol (200 cm3).
A yellowish white microcrystalline precipitate formed during the addition, which was found to redissolve on warming the reaction mixture to 50°C. The solution was cooled and stirred at room temperature for 30 minutes. The colume was then reduced to ca 200 cm3 in vacuo and the product was obtained as white crystals on cooling to -30°C overnight. The crystals were isolated from the reaction mixture by filtration under a nitrogen atmosphere and by successive washings with petroleum ether pre-cooled to 4°C. The crystals were pumped for 1 hour at room temperature to remove any volatile impurities. Overall yield was 93.6% (85.92g).
Microanalysis of the crystals suggested that the product had a limiting empirical formula (Et2Te)(CdBr2)2.
The pure adduct, (Et Te) (CdBr)2 , (85.92g, 0.092 g mol) was heated to 140°C. Pure diethyltellurium distilled and was collected in vacuo in a cold trap (14.66g, 0.0789 g mol, 85.85% yield). The adduct was found to dissociate between 80-90°C.
Preparative Example 5
Purification of diethyltellurium using Mercury (II) Iodide
A solution of diethyltellurium (4.78g 0.025 g mol) was added . dropwise to a red solution of mercury (II) iodide (6.16g, 0.013 g mol) in ethanol ( 250 cm3) to obtain a pale yellow crystalline product. The product was isolated from the reaction mixture by filtration under a nitrogen atmosphere and by successive washings with petroleum ether pre-cooled to 4°C. The crystals were pumped to remove any volatile impurities for 1 hour at room temperature.
Microanalytical data suggested that the product had a limiting emperical formula (Et2Te)2 Hgl2.
The pure adduct (EtTe)2 Hgl2 (5-90g, 7.146 m mol) was then heated to 150°C. Pure diethyl tellurium distilled and was collected in vacuo in a cold trap maintained at -196°C (1.22g, 6.573 m mol,
46.99% yield). The adduct was found to dissociate between 120-140°C.
Preparative Example 6
Purification of diethyltellurium using Mercury II Chloride
A solution of diethyltellurium (5.71g, 0.0307 g mol) was added dropwise to a solution of mercury (II) Chloride (7.39g, 0.0272 gmol) in diethyl ether (250 cm3) to obtain a pale yellow crystalline product. The product was isolated from the reaction mixture by filtration under a nitrogen atmosphere and by siccessive washings with petroleum ether precooled to 4°C. The crystals were pumped to remove any votalite impurities for 1 hour at room temperature.
Microanalytical data suggested that the product had a limiting empirical formula Et2Te HgCl2. The pure adduct Et T HgCl2 (11.65g, 0.0254 g mol) was then heated to 120°C. Pure diethyltellurium distilled and was collected in vacuo in a cold trap maintained at the liquid nitrogen temperature. The adduct was found to melt at ca 100°C and dissociate between 100-120°C.
Frerarative Example 7
Purification of di-isopropyltellurium using cadmium iodide
A solution of di-isopropyltellurium (61.48 g. 0.283 g mol) in diethyl ether (50 cm3) was aided dropwise to a solution of cadmium iodide (130.53 g, 0.3565 g mol) in ethanol (ca 250 cm3) to afford a clear orange solution. The reaction mixture was cooled to -30ºC overnight and the product was obtained as white needle shape-, crystals. These crystals were isolate! from the reaction mixture by filtration under a nitrogen atmeosphere, and by successive washings with petroleum ether precooled to 4ºC. The crystals were pumped for 1 hour at room temperature to remove any volatile impurities.
Microanalysis of the product suggested that the product had a limiting composition (i-C3H7)2Te.CdI2.
The pure adduct (192.06 g, 0.331 mol) was heated to ca. 130°C Pure di-isopropyltellurium distilled and was collected in vacuo in a cold trap maintained at -196°C. Yield was 31-26g, 5081 % based on the starting (i-C3H7)2Te.
Preparative Example 3
Purification of di-isopropyltellurium using cadmium bromide
A solution of di-isopropyltellurium (462 g, 0.0216 gmol) in ethanol (50 cm ) was added dropwise to a solution of cadmium bromide (CdBr2.4H2O, 9.91 g) in ethanol (50 cm%) A yellow-white microcrystalline precipitate formed during the addition The product was isolated from the reaction mixture by filtration under a nitrogen atmosphere and by successive washings with petroleum ether precooled to 4ºC. The cryεtls were pumped for 1 hour at room tempermature to remove any volatile impurities.
Hicroanalysis of the crystals suggestei that the product ha d a limiting composition CdBr2((i-C3H7)2Te)2.
The pure adduct (2.5 g) was heated to ca.125°C Pure di-isopropyltεllurium distilled and was collected in vacuo in a cold trap maintained at -196ºC. Yield was 1.oo g. 65.56 % based on the weight of the adduct
Claims
1. A method of purification of a tellurium or selenium alkyl characterised by forming an adduct of the alkyl with at least one compound of a group 11 or 12 metal (Cu, Ag, Au, Zn, Cd, Hg) and thermally dissociating the said adduct to yield the alkyl.
2. A method of purification according to claim 1 characterised in that the tellurium or selenium alkyl is a dialkyl.
3. A method of purification according to claim 1 or 2 characterised in that each alkyl group in the tellurium or selenium alkyl contains 1 to 4 carbon atoms.
4. A method of purification according to any one of claims 1, 2 or 3 characterised in that the alkyl is a tellurium alkyl.
5. A method according to claim 1 characterised in that the compound of a group 11 or 12 metal is a halide or nitrate thereof.
6. A method of purification according to claim 5 characterised in that the metal compound is a chloride, bromide or iodide.
7. A method of purification according to claim 6 characterised in that the at least one compound of a group 11 or 12 metal is selected from Cul, Cdl2, CdBr2, HgCl2 Cu2I2 and Hgl2.
8. A method of purification according to claim 1 characterised in that the adduct is formed by reaction between the alkyl and the metal compound in an organic solvent.
9. A method according to claim 3 characterised in that the solvent is selecte! from ethers, alcohols and nitriles and mixtures thereof.
10. A methoi of purification according to claim 1 characterised in that the adduct is dissociated at 80ºC - 150°C.
11. A method of purification according to claim 1 characterised in that diethyl tellurium is purified by forming an adduct with a compound selected from Cdl2, CdBr2, HgCl2, Cul2, and Hgl2 ani then thermally dissociating the adduct and collecting the alkyl.
12. A method of purification according to claim 1 characterised in that diisopfopyl tellurium is purified by forming an adduct with a compound selected from CdI2 and CdBr2 and then thermally dissociating the adduct and collecting the alkyl.
13. An adduct of dialkyl tellurium having a formula, selected from following:
((C2H5)2Te)2CdI2
(C2H5)2Te(CdBr2)2 ((C2H5)2Te)2CdBr2 ((i-C3H7)2Te)2CdI2 ((i-C3H7)2Te)2Cd-Br2 (i-C3H7)2TeCdI2
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB878728393A GB8728393D0 (en) | 1987-12-04 | 1987-12-04 | Method of purification of tellurium & selenium alkyls |
| GB8728393 | 1987-12-04 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0390833A1 true EP0390833A1 (en) | 1990-10-10 |
| EP0390833B1 EP0390833B1 (en) | 1993-02-10 |
Family
ID=10628000
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP89900285A Expired - Lifetime EP0390833B1 (en) | 1987-12-04 | 1988-12-02 | Method for purification of tellurium and selenium alkyls |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0390833B1 (en) |
| JP (1) | JPH0830056B2 (en) |
| KR (1) | KR0139104B1 (en) |
| DE (1) | DE3878465T2 (en) |
| GB (2) | GB8728393D0 (en) |
| WO (1) | WO1989005293A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8913799D0 (en) * | 1989-06-15 | 1989-08-02 | Secr Defence | Method for preparation of organotellurium and selenium compounds |
| KR101895666B1 (en) | 2016-05-18 | 2018-09-07 | 주식회사 서일 | Straw Attachment Device of the Rectangular Drinking Container and Method |
-
1987
- 1987-12-04 GB GB878728393A patent/GB8728393D0/en active Pending
-
1988
- 1988-12-02 KR KR1019890701468A patent/KR0139104B1/en not_active IP Right Cessation
- 1988-12-02 JP JP1500945A patent/JPH0830056B2/en not_active Expired - Lifetime
- 1988-12-02 EP EP89900285A patent/EP0390833B1/en not_active Expired - Lifetime
- 1988-12-02 WO PCT/GB1988/001062 patent/WO1989005293A1/en active IP Right Grant
- 1988-12-02 DE DE8989900285T patent/DE3878465T2/en not_active Expired - Fee Related
- 1988-12-02 GB GB8828190A patent/GB2213149B/en not_active Expired - Lifetime
Non-Patent Citations (1)
| Title |
|---|
| See references of WO8905293A1 * |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8828190D0 (en) | 1989-01-05 |
| DE3878465D1 (en) | 1993-03-25 |
| GB8728393D0 (en) | 1988-01-13 |
| GB2213149B (en) | 1991-07-17 |
| WO1989005293A1 (en) | 1989-06-15 |
| KR0139104B1 (en) | 1998-05-01 |
| DE3878465T2 (en) | 1993-06-03 |
| EP0390833B1 (en) | 1993-02-10 |
| GB2213149A (en) | 1989-08-09 |
| KR900700445A (en) | 1990-08-13 |
| JPH03501481A (en) | 1991-04-04 |
| JPH0830056B2 (en) | 1996-03-27 |
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